Former pilot describes re-entry path for shuttles

That's how Charles Bolden Jr., a former astronaut who twice piloted space shuttles to safe landings, described re-entry - the critical moments in which the Columbia exploded Saturday over Texas.

Bolden, a U.S. Marine brigadier general who said he had been riding his motorcycle Saturday in the Texas countryside near his home in Houston when Columbia broke up, spent 14 years in the shuttle program.

Bolden's first flight was on Columbia, but he was chief commander of Discovery and Atlantis, both of which he piloted, before leaving the program in June 1994.

As the re-entry phase begins, crew members suit up, buckle into seats, then the commander starts computer-controlled operations, which spin the craft 180 degrees and flip it a half-globe away from its destination.

Two thruster rockets then fire, bearing 6,000 pounds of force each to slow the shuttle from its orbiting speed of 17,580 mph to an eventual speed of 300 mph.

For a complete half-hour, Bolden said, "You are free falling" uneventfully. But gradually, the relative weightlessness that kept arms floating above armrests is replaced by the sense of "a couple of gorillas on your shoulders," he said.

It is during the final half-hour of re-entry that the outside of the space shuttle heats up to its highest temperatures: up to 2,400 degrees on the tiled underbelly and up to 3,100 degrees on the nose and wings.

Although the vehicle within maintains a comfortable 73 degrees, the outer glow, passing through stages of pink, orange and yellow, obscures most of the view out the windows. (Only the commander, sitting on the left, the co-pilot to his right and flight engineer in the middle and slightly behind, have a clear front-window view; those below deck have only a limited view out a side port.)

The final half-hour is "the most spectacular part" of the flight, Bolden said.

"The vehicle ... starts to glow, and you can't see out the front window," Bolden said. "It's as though you're seated inside a light bulb, trying to look out."

It takes 10 to 15 minutes for the glow to flare and recede before the most critical point in the mission takes place.

Here, the shuttle is "get- ting pretty close to maximum dynamic pressure and maximum thermal stress," Bolden said, "the most risky" part of the re-entry.

At this phase, Bolden said, is when Columbia appears to have broken up.

Critical at this point, Bolden said, is maintaining the craft in what pilots call the "slip stream." The shuttle at that phase is still piloted by computers, which maintain the course with pin-point accuracy in an aerodynamically stable direction.

Bolden, though, said astronauts are trained at piloting the craft themselves through this phase. Having done it in training, Bolden likened it to "a plane trying to balance itself on a ball."

Bolden declined to conjecture on specific causes for the Columbia disaster, but he knew from his four shuttle flights on three different craft that one thing was certain.

"Whatever happened, happened very quickly and very catastrophically," Bolden said.